This is a modern affliction, brought to us by the ubiquity of automated spell-checkers (curse them!)
In days gone by, people had to proof-read what they had written before it was (expensively) committed to public view. But now, when the spell-checker gives your prose a clean bill of health, you are subtly tempted to assume that it actually
is what you intended to write and to not bother reading what is really there.
Sadly, even if your magnum opus
doesn't have any words underlined in red, you cannot then draw the conclusion that it is without error.
In my experience, spelling checkers cause two types of problem: They fail to highlight use of the wrong variant of a word (there/their etc.), and they also fail to draw your attention to missing words.
On many occasions I have finished a paragraph, then on reviewing it, while still basking in the internal wonder of the idea I was trying to convey, found to my horror that I had missed out whole phrases as my mind raced on ahead of my typing.
By the way, great guide

, I hope you are going to extend it with tips on how to write clearly at a scale larger than the sentence (like how to organise paragraphs etc.).
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